1. Field of the Invention
The present invention relates to an improvement in an electronic circuit device having an electric-code locking function (hereinafter abbreviated as "electronic circuit").
2. Description of the Background Art
FIG. 1 shows the configuration of this type of conventional electronic circuit device. In FIG. 1, reference numeral 1 indicates an antenna 1. Designated at numeral 2 is a radio receiving circuit for receiving a radio broadcast from the antenna 1. The radio receiving circuit 2 comprises a high frequency amplifier, a local oscillator, a mixer, an intermediate frequency amplifier, a detecting circuit, a noise killer circuit, a multiplexing circuit, etc. Designated at numeral 3 is a tape circuit which comprises a tape deck and an equalizing circuit.
Designated at numeral 4 is a signal switching circuit for selecting either one of signals output from the radio receiving circuit 2 and the tape circuit 3. Reference numeral 5 indicates a muting circuit supplied with the selected signal and for effecting a muting operation. Reference numeral 6 indicates a low frequency amplifying circuit for amplifying the output of the muting circuit 5, and reference numeral 7 indicates a speaker electrically connected to the low frequency amplifying circuit 6. Designated at numeral 8 is a power supply detecting circuit for detecting whether or not a battery 15 used as a power supply is electrically connected to the electronic circuit device through a connector 14. Reference numeral 10 indicates a mnemonic code holding circuit comprised of a non-volatile memory or a diode matrix or the like used to store mnemonic codes therein in advance.
Designated at numeral 11 is a control input unit for inputting mnemonic and collating codes and for controlling a radio, for example. Reference numeral 12 indicates a displaying driver and reference numeral 13 indicates a display for displaying the frequency received by the radio, for example. Designated at numeral 14 is a connector electrically connected to the inputs of the control circuit 16 and the power supply detecting circuit 8. Reference numeral 15 denotes a battery electrically connected to the connector so as to be detachable from the electronic circuit device. Reference numeral 16 indicates a control circuit which has inputs electrically connected to the power supply detecting circuit 8, the mnemonic code holding circuit 10, the control input unit 11 and the connector 14 and which effects various control of the radio receiving circuit 2, the tape circuit 3, the muting circuit 5 and the displaying driver 12 in response to their corresponding input signals.
The operation of the electronic circuit device will next be described below. When the electronic circuit device is in a normal operation state, the control circuit 16 controls the radio receiving circuit 2 and the tape circuit 3 in response to an operation signal input from the control input unit 11 and provides control so as to bring the muting circuit 5 to a non-operation state. Further, the control circuit 16 drives the displaying driver 12 so as to display the received frequency or the like on the display 13. On the other hand, the signal switching circuit 4 selects either one of the signals output from the radio receiving circuit 2 and the tape circuit 3. The selected signal passes through the muting circuit 5 and the low frequency amplifying circuit 6 so as to be output from the speaker 7 as an acoustic signal.
When the electronic circuit device is first connected to the battery 15 or when the electronic circuit device is re-connected to the battery 15 after it has been disconnected from the battery 15, the power supply detecting circuit 8 detects that the battery 15 used as the power supply has been connected to the electronic circuit device. In response to the detected signal output from the power supply detecting circuit 8, the control circuit 16 then detects if the electronic circuit device has been disconnected from the battery 15, i.e., it has been stolen.
The control circuit 16 is activated upon detection of disconnection so as to bring the muting circuit 5 to an operation state and to bring the radio receiving circuit 2 and the tape circuit 3 to a non-operation state until a code identical to one of the mnemonic codes which have been stored in the mnemonic code holding circuit 10, is input from the control input unit 11, thereby prohibiting the electronic circuit device from operating. If a proper code is input before the execution of, for example, a third input operation by the control input unit 11, then such a prohibited state is unlocked. When, however, mnemonic codes are continuously misinput three times, for example, the prohibited state is locked.
A description will next be made of a mnemonic code process of the control circuit 16 with reference to FIG. 2. When the power supply is turned on in Step S1, the control circuit 16 makes a judgment, based on the result of detection by the power supply detecting circuit 8, as to whether or not the electronic circuit device has been disconnected from the battery 15, that is, the electronic circuit device has been stolen. If the answer is determined to be No, then the routine proceeds to Step S10 where the electronic circuit device can be normally operated.
If, on the other hand, the answer is determined to be Yes in Step S2, then the routine proceeds to Step S3 where a message of "CODE" is displayed on the display 13 and a waiting state for input of a mnemonic and collating code is entered. Next, in Step S4, codes such as numerals corresponding to preset channels are input from the control input unit 11 by pressing the preset channels of a radio, for example. The input codes are successively displayed on the display 13.
When all the mnemonic and collating codes are input, one of the mnemonic codes, which have been stored in the nemonic code holding circuit 10, is compared with one of the codes referred to above in Step S5. If it is determined that the proper mnemonic and collating code has been input, then a failure counter is reset in Step S9. The routine then proceeds to Step S10 where the electronic circuit device can be normally operated.
If, on the other hand, it is determined in Step S5 that the input mnemonic and collating code differs from the mnemonic code and is erroneous, then the routine proceeds to Step S6 where the failure counter is incremented by +1. It is thereafter determined in Step S7 whether or not the count of the failure counter is equal to a positive integer n (n=3, for example). If the answer is determined to be No, then the routine is returned to Step S3 wherein subsequently a desired code is reinput. If the answer in Step S7 is determined to be Yes, it is then judged that the mnemonic and collating code has not been properly input n times. Therefore, the muting circuit 5 is brought to an operation state, and a message of "OFF" is displayed on the display 13 in a state in which the radio receiving circuit 2 and the tape circuit 3 remain nonoperational. Thus, the electronic circuit device is brought to a locked state shown in Step S8 in which all the operations other than the turning ON and OFF of the power supply are prevented.
In the above conventional example, the mnemonic code has been stored and set up in advance. However, an electronic circuit device is known which can be provided with backup power and which enables the input and set-up of mnemonic codes, as has been disclosed in Japanese Patent Application Publication No. 3-3974, for example.
The conventional electronic circuit device has been constructed as described above. Thus, when the normal operation is effected after the electronic circuit device has been stolen, a code, which coincides with a mnemonic code peculiar to the electronic circuit device, must be input. Therefore, when the electronic circuit device is activated to check its operation or the like upon its fabrication, it is necessary to input individual different mnemonic and collating codes, thereby causing a problem that the work efficiency is impaired.